(1) Field of the Invention
The present invention relates to a printing plate which can be easily handled in a light room and is superior in vacuum contact with an image pattern.
(2) Description of the Prior Art
Printing plates are required to be improved in sensitivity and resolution, and researches and development thereof have been made positively. On the other hand, with improvement of those characteristics, there is an increasing tendency to the demand for accuracy of handling in the exposure (meaning irradiating light which is effective to induce a photoreaction of a printing plate, to a front side through an image pattern for the purpose of forming the image thereon, hereinafter referred to simply as "exposure", the "front side" indicating a surface to be exposed to light for image formation) and developing steps. More particularly, in order for the printing plate to fully exhibit its characteristics it is dustproofing and light shielding. Especially as to shielding the active light, even a slight fogging to active light other than image forming exposure is not allowable. It would impair the characteristics of the printing plate, so it has recently become necessary to make a strict control of the illumination environment.
However, the stricter the illumination environment (e.g. precision works under a yellow or red lamp to shield light which is effective to induce a photoreaction of the printing plate), the greater becomes the visual fatigue of the worker. To avoid this inconvenience, there are many users who desire to work in a light room.
Where the printing plate is exposed to light through a positive or negative image pattern, vacuum contact is usually performed in order to enhance the contact to the image pattern. In this connection, it is known that various uneven treatments or irregular treatments are applied to the front side of the printing plate with a view to improving such contact. However, if these treatments are performed to excess for the said purpose, the scattering of light will be increased during exposure, resulting in deteriorated reproducibility for image patterns, although the contact to the image pattern will be improved. Thus, it is difficult to keep the balance.